Accurately detecting the size and/or presence of particles is advantageous in many technologies and industries, including food processing, materials manufacturing, biotechnology, environmental, and medical testing. Measuring random changes in the intensity of monochromatic collimated light from a laser, which is scattered from a suspension or solution is a known technique for particle size distribution detection and changes in particle sizes or distribution during aggregation, dissolution, crystallization, or coagulation events. The currents state of the art optical instruments for measuring particle size include dynamic light scattering (DLS), photon correlation spectroscopy (PCS), nephelometry, and quasi-elastic light scattering (QELS). All of these techniques involve illuminating particles with monochromatic, collimated light and employ planar or cylindrical sample chambers between the source (a laser) and the detecting unit. In scattering media, the intensity of scattered light collected at different angles is a function of particle size, the wavelength of incident light, and the relative refractive index of the liquid or suspension medium and suspended particles. Laser light illuminates the sample that is enclosed in a sample chamber or cell, and the scattered light signal is collected with a detector placed at an angle with respect to the laser beam entering the sample chamber. However, the current state-of-the-art particle sizing technology is unable to utilize the presence of caustics. Some of the advantages that Applicants have discovered in the use of caustics in measuring particle size includes achieving faster results without the need for expensive sophisticated equipment (e.g., mirrors, lens, amplification, light splitting, monochromated light sources).
For example, in U.S. Pat. No. 7,268,874, a method of measuring properties of particles immersed in a body that includes performing a series of instantaneous acquisitions by illumination of the body with a temporally coherent light beam of predetermined width D and predetermined wavelength □ so that the light beam interacts with the particles by generating scattered radiation, and the detection of a plurality of values of the intensity of the total radiation. However, U.S. Pat. No. 7,268,874 fails to teach the use of caustics to focus light with droplet to form an optical caustic and amplify the light by droplet geometry as demonstrated in current invention. Many techniques known in the art simply do not suggest using caustics and instead require mirrors for re-emitting of light (as in U.S. Pat. Nos. 8,174,773, 7,187,441, and 5,815,611), the use of amplifiers (as in U.S. Pat. No. 6,796,195), special screening members (as in U.S. Pat. No. 8,123,040), or other expensive and sophisticated equipment. See U.S. Pat. No. 6,738,144 (teaching the use an interferometer for particle size determination); U.S. Pat. No. 5,627,642 (teaching the use of a length of a gradient index multimode optical fiber fusion spliced to a monomode optical fiber). Other techniques do not use optical caustics at all, either in catacaustic or diacaustic forms. See, e.g., U.S. Pat. No. 7,331,233 (teaching the use of ultrasound attenuation).